My Forester starts and idles @ up to 2,000RPM (!) for a few moments. As it idles down, the idle gets very rough. The piston-slap that was there before (I think), seems more pronounced as well.
ODO reads about 144,000 miles. 2.5L SOHC w/ an auto trans
*newer plugs, wires, fuel filer
*new head gaskets, timing belt, idler pullys, TB tensioner, water pump, upper/lower radiator hoses, coolant, thermostat, accy belts
*professionally cleaned and milled heads with adjusted rockers and ground valves
I'm about at wits end. (As well as the end of my checking account!) The dealer did a diagnostics check and told me about the knock sensor and the pre-cat O2 sensor, which was good! I really doubt that the O2 sensor is going to do this. I cannot find any hoses that I missed after reassembling the engine.
Anyone have any idea's?
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Subarus tend to block their radiators. Often there is only 10% or less flow. The radiator needs to be taken out and have a radiator shop strip and rod out the core tubes or fit a new or recored radiator.
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sounds like low compression at start up do to piston slap and not alowing car to warm up over the years before driving off. 3.1, 3.4, 3.5 motor pistons are exact size at operating temp there for cold temps at start up cause the pistons to slap the cylinder wall.. Gm engineers did this to reduce operating temp while driving by lowering friction in the cylinder. problem is most people these days start there cars and take off down the road..my suggesting would be to check piston compersion at operating temp and see if it meets spefications for ur mottor before replacing any other parts...
It may be piston slap. This is caused by either engine wear with the piston bores being too large for the pistons, or by poor manufacturing tolerances, or a combination of both.
To test for this, start the engine up first thing in the morning and run it for about thirty seconds while you listen carefully and memorise the sound and
intensity. Turn the engine off quickly, remove the spark plugs and put two
squirts of motor oil into each cylinder. Reinstall the plugs, start the
engine up again and listen. If you have piston slap the noise will have been greatly reduced or even
eliminated for about thirty seconds seconds and then returns.
The fix is to rebuild or replace the engine, but if it works just fine then don't worry. Many slappy engines keep going for tens of thousands more mile. The fact that your knocking is only at idle suggests your crankshaft is not to blame.
Did you replace the plugs with the same plugs (Manufacturer) as the plugs you had in there. Some cars are very picky with plugs. ie: some Japanese cars will only run well with NGK Spark Plugs. Try to use only what Subaru recommends in your engine for the best performance.
it could be that the tick over is two slow in brive,,,
set it up to tickover at 850,,950 rpm (in drive)
or it could be a gear box fult like the drive plate has a crack in it,,,letting the torque converter slap about,,,
chech tick over first,,, bont adjust tick over in gear unless the brakes are held hard on,,,
sounds like the air idle valve , if you can get hold of valve to test, try this find valve on inlet manifold and pull hose off going to throttle body,reconect hose to new valve so valves are i line to each other, start car and let it idle for a few moments till the fast idle slows down, then disconnect the wirering goint to the original aiv and connect to the new one , hopefully the original one would have been diconnected in the open position , reconnect wirering to the new valve and turn engine off. disconnect battery for 20 seconds . recon battery and turn ignition on, pump gas pedel 5 times to reset . start engine and let it idle for a few moments ,then try to turn steering wheel , engine speed should rise slightly due to load from power steering pump and then settle back down 875 1075 rpm.this is what the air idle valve should do. if it doesen't look at wiring goig to aiv might have scuffed through.
I have the same problem on my 2.0L 2001 Legacy auto. It began about 1000 miles ago. It has now done 84k. From my online searches this is most probably 'piston slap', and is not serious. To save weight Subaru shaved down the skirts on the pistons. With normal engine wear the pistons will at some point rattle against the cylinders until the engine is heated up and the pistons expand. The rattling should go away after a few minutes. If it persists say 10-15 minutes, it may be another problem.